Most desktop computer systems utilize a handheld pointing device referred to as a “mouse”. The mouse provides a signal to the computer indicating the amount the mouse has been moved over the desktop since its last report. The displacement of the mouse is used to control the displacement of a cursor on the computer screen. Typically, the cursor moves from its current location to a new location having a displacement that is related to the measured displacement of the mouse on the desktop.
The mouse also typically includes a number of buttons or wheels that are used to signal the computer. For example, one of these buttons typically causes the computer to select an item on the screen that is under the cursor when the button is pushed. A second button is often used to display a short menu on the screen having commands that the user can execute.
Early mouse designs utilized a ball that rolls against two encoders as the user moves the mouse over the desktop. The output of the encoders provides a measurement of the distance traveled by the mouse. While this mouse design provided an inexpensive pointing device, it had a number of problems. First, the ball picked up grease and other debris from the surface of the desktop and transferred this material to the rollers used in the encoders. Over time, the buildup of the debris on the rollers resulted in a degradation in the performance of the mouse, and hence, the mouse required periodic cleaning. Second, the mechanical nature of the device made it difficult to reduce the cost of the device beyond a certain point.
As a result of these limitations and the decrease in cost of semiconductor imaging arrays and processors, the optical mouse was introduced. An optical mouse includes a “camera” that periodically takes a picture of the surface under the mouse. The successive pictures are compared to one another to determine the distance that the mouse moved between pictures. The device has no moving parts, and hence, the difficulties associated with the mechanical mouse are substantially reduced. In addition, the camera is recessed with respect to the bottom surface of the mouse, and hence, the camera does not become fouled by grease and other debris on the desktop surface.
The cameras used in optical mice are typically constructed from silicon imaging arrays to reduce the cost of the camera. Silicon imaging arrays have their maximum sensitivity in the wavelength range from about 600 nm to 100 nm, and are most sensitive in the region from 800 nm to 900 nm. The red LEDs used in optical mice typically emit light in the range of 620 to 660 nm. Hence, prior art optical mice have a less than optimum match between the LEDs used to illuminate the surface and the silicon imaging arrays used to form the image. As a result, the power requirements of the mouse are increased. The power needed to operate the mouse is particularly important in wireless optical mice, since batteries must supply the power.
In addition, optical mice typically emit a flashing red glow. To minimize power consumption and to provide an electronic shutter, the LED is only turned on when an actual image of the surface is being formed. When the light is turned on, a portion of the light often escapes the mouse. Some mouse designs specifically allow a portion of the light to escape to enhance the appearance of the mouse. Some users find the color less than appealing. In addition, the flashing light can be distracting.